In the modern manufacture of glass fibers, a method of manufacture known as the direct melt method is employed. In this method of preparing glass fibers, the glass batch ingredients in powdered or granular form are introduced into a furnace and melted. The molten glass resulting from the melting operation is passed from the furnace through a refining section to elongated forehearths. Fiber glass forming bushings located below the forehearths are attached at many points along the length of the forehearth to provide positions along the forehearth from which various fiber glass products are formed. In FIG. 3 of U.S. Pat. No. 3,837,823, a diagramatic illustration of a melter, refiner and forehearth with bushing openings is shown. In the same U.S. patent, the typical bushing connection to forehearth refractories is also shown.
As will be appreciated, glass batch ingredients which are melted in the furnace in a direct melt operation travel a considerable distance in passing through the furnace, the refining section and the elongated forehearths from which the various fiber forming bushings depend. The furnace itself, the refiners and the forehearths are all lined with refractories that are typically constructed of high temperature resistant materials such as chrome oxides and zircon materials. During the course of a furnace campaign which can last from 3 to 6 years, the molten glass passing over the refractories contained in the melting chambers, refiners and forehearths are subject to erosion and attack by the molten glass which frequently introduces particles of the refractories into the glass melt and they ultimately reach the bushings. These refractory particles, being extremely high temperature resistant refractories, are difficult to melt and therefore, find their way into the fiber forming bushings as solid particles.
The fiber forming bushings utilized to produce the glass fibers are generally rectangular vessels. These bushings are fabricated from precious metals or precious metal alloys such as platinum or platinum-rhodium alloys. Characteristically the bushings have four sides and a bottom on which are positioned a plurality of nozzles or tips through which the molten glass fed to the bushing emanate to form individual streams of molten glass. These streams of molten glass are formed into fibers as the molten glass exits the bushing. The bushings are also characteristically open at the top and contain a side flange around the perimeter of the bushing which is utilized to attach the bushing to the refractories contained in the forehearth opening.
Any refractory particles present in the molten glass, known in the art as stones, enter the bushing in a flowing column of glass from the forehearth and are carried down into the bushing bottom where, if the stones are of sufficient size, they plug up the nozzles or tips causing a break out of the bushing position. If several nozzles or tips of a bushing become clogged with unmeltable, solid, refractory particles the number of filaments produced at a given bushing is subsequently reduced and an unsatisfactory product is then obtained from that bushing.
In a typical fiber glass operation, the filaments formed by the exit of molten glass at the bushing tips or nozzles are passed over an applicator which applies a desired chemistry to the glass surfaces, they are then gathered into a strand form by passing them through a grooved gathering shoe. The strand is then collected usually on a winder. In some instances, the glass being drawn by the collecting device is chopped into discrete lengths utilizing a chopper rather than a winder. In any event, if particulates of refractories block or clog the bushing nozzles or tips, the bushing position becomes unsatisfactory for the production of a particular type of strand since it will not have the required filament count or the bushing itself will flood in the areas of the clogged tips. Ultimately flooding will involve other nozzles or tips that are still running and eventually the bushing position will no longer function properly. This will require a shut-down of the bushing position for replacement of the bushing.
Thus, a need exists in the art to insure in a direct melt operation that unmelted refractory particles that would normally interfere with a bushing nozzle or tip are eliminated before such materials reach the bushing bottom or faceplate as it is known in the art so that they do not clog the openings for the nozzles and tips contained in the bottom of the bushing and/or interfere with glass flow from the bushing.